Suzuki RG500 Gamma Road Test

In 1984, a Yamaha advert quite boldly stated “ No one has ever built a road machine so close in technical basis to a current GP winner. Quite frankly we do not expect that any one else ever will”.

How wrong they were and just one year later they had good cause to regret that statement as the Suzuki RG500 burst onto the scene. Thankfully Suzuki were brave enough to give us not only the visual image, but also a real taste of GP performance with the Gamma. Endowing the machine with plenty of fire from within its four-pot belly, rather than the somewhat castrated, and over weight effort that Yamaha made with the RD500.

Place the RD500, NS400 and RG500 Gamma side-by-side and you would have three of the top manufacturers attempts at producing a replica of their respective GP racers, however, with all but one of those machines, all you purchased was a mere shadow of the original design. That is not to say the others were rubbish, far from it in fact, but the RG was definitely nearer the mark, and actually far closer to the race machine than you might ever imagine.

The Suzuki is almost an exact replica of the race machine, its roots can be traced directly to the 1983 factory XR45 and the crankcases, barrels and general engine layout are virtually identical to the bikes ridden by Sheene, Mamola, Crosby and the rest of the factory boys.

The bore and stroke is identical in design to the race machine, as indeed are most of the engine components although a shock damper was added to the lay shaft to reduce loads between the cranks and the clutch/ gearbox. Starting the engine is achieved by kick-starter and, unusually for a Japanese machine, as the mechanism does not drive the clutch outer gear, but the input shaft of the gear box, the engine has to be started in neutral rather than simply leaving it in first and holding the clutch in.

The engine breathes through four flat-slide Mikuni VM28SH, mounted like the racer in pairs either side of the engine. When viewed from the side these carburettors are incredibly short, only 36mm, and is key to good power from a disc-valve engine. Just like the real racer the gearbox is a cassette type and can be removed in double quick time giving access to the gear wheels enabling different ratios to be fitted for all of the gears. The factory race bikes of 83/84 could utilise up to six different ratio’s for the first four gears and five for fifth and sixth and this feature was retained for the roadster. The ratios chosen for the roadster gearbox are, apart from the ridiculously high first gear, pretty well matched for high-speed use, although the five locating dogs on each pinion do slow down the selecting mechanism somewhat.

It would be reasonable to assume that, although no race kit was announced or in fact produced by Suzuki at the launch of the Gamma, it was obviously originally designed to accept go faster goodies, thus creating a formidable production class race bike. A theory suggested by Graham Dyson, whose UK based company, Nova designed and built a race gearbox for the RG, was that the Gamma was so close to the RG, the factory correctly assessed that a race kit would detract sales from the real thing by providing a much cheaper yet still competitive alternative.

All this power was managed by the Suzuki Automatic exhaust control (SAEC), which utilised a servo power gate that opened up a chamber in each barrel/ head assembly increasing the volume of the exhaust down pipe. The SAEC valve is controlled by the AEC box, fed by signals from the CDI box, then via a stepper motor and cables to the valves. These rotary valves only actuated below 7500rpm by which time they would be fully opened up. This was Suzuki’s variation on the YPVS exhaust valve, and Honda’s ATAC system. The SAEC gave the Gamma an impressive spread of power with good pull available from 5000revs with things getting really serious at 7000 before shooting completely through the 10,000 redline to a worrying, but non the less fantastically exciting, 12k According to the Suzuki published power curves there is no actual increase in power above 9500rpm, but it certainly does not feel like that when riding the RG.

Exactly like the race machine, the four water-cooled cylinders are arranged in a square above two stepped crankshafts, with the pistons set at 180 degrees to each other so that they fire in opposite pairs, giving perfect mechanical balance. So smooth is the running of the Gamma that, unlike the 50-degree V-four layout of the Yamaha 500LC, no power sapping balance shafts are required to dampen out vibration, saving much weight and space in the process. The RD will lose something like 8bhp just because of the balance shafts.

Power is plentiful and with a little fettling can be improved enormously. Mildly tuned machines have recorded as much as 108bhp and 55ft lbs of torque. A common mod is the fitting of aftermarket pipes and these can, with a little rejetting, instantly transform your machine. The main reason for this is the original manufacturer has to comply to various limiting noise regulations at certain engine revolutions whereas the after market guy doesn’t.

Total weight for the Gamma was a rather portly 154kgs, but this is due to the equipment required to make it road legal, with this removed the weight soon drops to a more competitive 130kgs. Surprisingly in standard form the Gamma is actually 9kgs lighter than the Honda NS400R. The aluminium square section frame, constructed along the same lines as the GSXR 750 but with a much heftier steering head, held everything nicely in place and gave a very precise ride, the massive steering head doubles up as the entrance to the six-litre air box and filter housing.

The handling is very good particularly on a track although the sixteen inch front wheel sometimes makes the RG a little frisky when on the bumpy, pot hole ridden, queens highway. By today’s standards the tyres, 110/90V 16” front and 120/90V 17” rear are skinny but back then this was the very forefront of chassis design. The front forks where the usual telescopic oil damped units with spring pre load adjustment, air valves and the dreaded “anti dive” mechanism, although this one worked reasonably well, located on the front of each fork slider. The rear “Full-floater” suspension system, operated by a rocker arm assembly, was adjustable via a remote knob. For such an agile machine the head angle is a lazy 30deg, with a largish trail of 110mm too. Two 260mm floating discs grabbed by a pair of 4 pot calipers, identical to the GSXR750 of the time, providing the stopping power, with a much smaller rear disc and basic caliper performing the duties at the rear.

In 1986 Padgett’s of Batley began development of a Gamma based TTF1 machine. Having already experimented with the overweight Yamaha, Padgett’s turned their thinking to the Gamma as a potential contender. The F1 rules of the time allowed 1000cc four stroke and 500cc two stroke road based machines, and from the very beginning of development the Padgett’s RG Gamma was competitive, producing power and speed not far off the performance of the real thing. At Hockenheim, that season, the Gamma passed the speed trap at 171mph while the pukka race RG clocked 173mph, a mere 2mph difference.

Lincoln rider, Mark Phillips convincingly won the Shell Oils TT F1 championship in 1986 on the Padgett’s Gamma amongst a sea of FZ750 Yams and GSXR Suzuki’s. Mark remembers “The F1 bike was something very special indeed, actually lighter than the MK10 RG I was racing in the open classes. At Assen, after fitting a race ignition, I had to keep backing off the throttle because it was revving so high I thought it would blow up, of course it never did. In that championship year we only had one mechanical misdemeanour when a gear broke at Mallory and spat me off, after then the problem was sorted and she ran all season”.

A very special Gamma indeed

With out doubt the most famous person to race a 500 Gamma was Kevin Schwantz, already an established star in the US, Schwantz was keen to make a favourable impression with the European GP bosses. Schwantz had already set the UK scene alight earlier that year when he stormed the Transatlantic challenge on a GSXR750 and was poised to make a similar impact on the GP circuit. For TT F1 World round held at Assen, the US rider rode a virtually standard 500 Gamma literally taken out of stock at Suzuki GB and race prepped the week before.

Chief Suzuki race technician at the time, Martyn Ogbourne takes up the story, “No engine modifications were carried out, there simply was not time, just the removal of unnecessary parts, lights etc and the fitting of competition tyres. Assen is deceptively fast with a Donington Park like string of corners, I knew the bike would be out paced in a straight line but relied heavily upon Schwantz and his undoubted riding ability. The gearing required for Assen is identical to both Daytona and the TT with top speeds in excess of 190mph being the norm in the big bike classes.”

The future 500 World Champion finished an impressive second behind Joey Dunlop and his factory V-four Honda. Ogbourne “I had assessed that, with the right jockey on board, the Gamma would lose around three places per lap down the straights but then make up five around the sweeping twisty bits”. Just as amazing is the end to the story, following the Assen race, the RG500 Gamma was returned to standard road going trim, placed back into stock and then sold having had only the one “careful owner” from new.